In the fabrication process of an IC device, various material layers are deposited on a semiconductor substrate for different purposes such as for insulation, for electrical conduction, for passivation, etc. After the deposition of a material layer is conducted, the physical properties of the layer sometimes must be determined in order to ensure the reliability of the device fabricated. For instance, in the fabrication of an EPROM (electrically programmable read only memory) devices, a passivation layer of silicon oxynitride is frequently deposited on top of a finished device for passivation purpose. Furthermore, as a final processing step, an UV light is used to erase memory in the EPROM chip. The UV transmittance property of the final passivation layer of silicon oxynitride is therefore an important property that must be determined before a large number of wafers can be processed.
Conventionally, the UV transmittance of a material layer coated on a semiconductor wafer is conducted in a test apparatus 10 shown in FIG. 1. The test apparatus 10 is commercially supplied by the Hewlett Packard Company of Palo Alto, Calif. In the test apparatus 10, an upper platform 12 is mounted spaced-apart from a lower platform 14 by a backing plate 16 and two support columns 18. The upper platform 12 and the lower platform 14 are mounted in a parallel relationship. Mounted between the upper platform 12 and the lower platform 14 is a light reflectance device 20 that consists of two reflecting mirrors 24, 26 each with a planar surface. An incident UV beam 28 is emitted from an UV source (not shown) and is reflected upwardly by the first mirror 24 toward a window 30 in the upper platform 12. A semiconductor substrate (not shown) is positioned on the top surface 22 of the upper platform 12 with a surface to be measured facing the reflected UV beam 32. The UV beam 32 is reflected again by the surface of the semiconductor substrate into a reflected beam 34 toward the second mirror 26. The reflected UV beam 34 is finally reflected by the second mirror 26 into UV beam 38 which is received by an UV receiver/analyzer for determining the UV transmittance (or absorption) of a coating layer on the surface of the semiconductor substrate.
The test apparatus 10 shown in FIG. 1 presents several processing difficulties. First, the semiconductor substrate is positioned face down on the surface 22 of the upper platform 12 for making measurements. In order to obtain an accurate measurement, different locations on the surface of the semiconductor substrate must be measured. In the conventional apparatus 10, different measurement locations cannot be determined since there is no provision for determining such positions. Secondly, when the substrate is moved around on the surface 22 of the upper platform 12, surface scratches are inevitable which seriously affects the quality of the IC devices in the substrate. The conventional test apparatus 10 is therefore inadequate in making accurate measurements and in preventing damages to semiconductor substrates being measured.
It is therefore an object of the present invention to provide an apparatus for measuring optical properties of a coating layer on a substrate that does not have the drawbacks or shortcomings of a conventional apparatus.
It is another object of the present invention to provide an apparatus for measuring optical properties of a coating layer on a semiconductor substrate that can be used to obtain accurate and reliable data.
It is a further object of the present invention to provide an apparatus for measuring optical properties of a coating layer on a semiconductor substrate that does not damage the surface of the substrate during such measurement.
It is another further object of the present invention to provide an apparatus for measuring optical properties of a coating layer on a semiconductor wafer that utilizes a fixed stage and a traversing stage for moving a substrate on the fixed stage.
It is still another object of the present invention to provide an apparatus for measuring optical properties of a coating layer on a semiconductor substrate capable of mounting a substrate in a traversing stage such that the substrate surface to be measured does not have direct contact with the measurement apparatus.
It is yet another object of the present invention to provide an apparatus for measuring optical properties of a coating layer on a semiconductor wafer that utilizes a fixed stage with pre-marked index locations on the stage such that measurements can be indexed and repeated for high accuracy.
It is still another further object of the present invention to provide a method for measuring optical properties of a coating layer on a semiconductor wafer by mounting the wafer in a traversing stage which slidingly engaging a fixed stage and projecting an UV beam through a window in the fixed stage.
It is yet another further object of the present invention to provide an apparatus for measuring UV transmittance of a passivation layer on a silicon wafer by mounting the wafer in a traversing stage and then moving the traversing stage on a fixed stage provided with indexing marks such that measurements can be made at predetermined locations on the wafer.